Hydra-RDF

hydra-rdf is the translingual RDF support package for Hydra. It is generated into Haskell, Java, Python, and TypeScript from a common set of DSL sources, and depends only on hydra-kernel.

For background on how Hydra relates to RDF and SHACL, see the RDF wiki page.

What it provides

• RDF 1.1 syntax model — IRIs, literals, blank nodes, triples, graphs, datasets.
• SHACL syntax model and coder — maps Hydra types to SHACL shapes and Hydra terms to RDF descriptions (the data triples that conform to those shapes).
• OWL 2 syntax model — full coverage of OWL 2 classes, properties, individuals, and axioms. Syntax only; there is no OWL coder yet.
• ShEx syntax model.
• XML Schema syntax model.
• N-Triples serializer (rdfGraphToNtriples) — the only output format currently supported. Reading (parsing) of any RDF format is not yet supported.
• Eclipse RDF4j overlay (hydra.overlay.java.rdf.SerdeNative) — a host-native Java integration that serializes Hydra RDF graphs (hydra.rdf.syntax.*) via RDF4j's Rio writers (and supports the reverse). Hand-written, host-specific code: it lives under overlay/java/hydra-rdf/ and is copied onto the generated distribution at assembly time (#511; formerly the separate bindings/java/hydra-rdf4j artifact). Its third-party dependency (org.eclipse.rdf4j:rdf4j-rio-ntriples) is declared in overlay/java/hydra-rdf/build.json.

Demos

Three demos exercise this package end-to-end:

• demos/shacl — generates SHACL shapes from the Hydra kernel types, encodes kernel modules as N-Triples, and validates the data against the shapes.
• demos/avro — bidirectional Avro coder; the included AvroWorkflows tool transforms Avro-schema'd JSON data into SHACL RDF.
• demos/genpg — generates a property graph from relational CSV data and emits it as either GraphSON or RDF/SHACL N-Triples.

N-Triples output

The serializer follows the N-Triples 1.1 specification. Literals preserve all Unicode verbatim and escape only ", \, LF, and CR. IRIs emit any of the spec-disallowed characters (controls and <>"{}|^\) as \uXXXXUCHAR escapes; all other code points pass through. Earlier versions replaced any non-ASCII character with?`; that bug was fixed in #363.